1. Field of Invention
The invention is related to a railway vehicle wheel comprising a hub and a tire provided with a flange, which hub and tire are mutually connected by means of a disc or a number of spokes.
2. Description of Related Art
In operation, the contacts between rails and railway constitute sources of vibrations which are transmitted to the wheel shaft. Consequently, these vibrations are also imposed on the bearings and finally the superstructure of a train wagon or locomotive. They are experienced by the passengers and train personnel as unpleasant; moreover, fatigue of the steel material of the wheels and shafts may be aggravated thereby.
From U.S. Pat. No. 5,183,306, a railway vehicle wheel is known comprising a rubber ring situated between the hub and the tire of the wheel. In a radial cross-section, said ring has an U-shape, leading to radial shear of the rubber material. The ring has a large thickness, of the same order of magnitude as the tire.
A disadvantage of this known railway vehicle wheel is its rather great radial resilience, and the complicated structure with separate connecting rings and bolts.
The object of the invention is to provide a railway vehicle wheel having improved damping properties, while maintaining its stiffness. This object is achieved in that the tire comprises a thin visco-elastic layer for dissipating vibrations originating from the contact with a railway track.
In the rail wheel according to the invention, visco-elastic material layer is applied that dissipates energy under shear. In particular, vibration energy is thereby damped out quickly despite the small thickness of the layer. Said thickness is of a smaller order of magnitude than the thickness of the tire.
According to the invention, the visco-elastic layer is loaded under shear in the circumferential (or tangential) direction, which provides the required relative displacements in the rubber layer for obtaining the desired damping properties.
Preferably, the visco-elastic layer is circular and concentric to the tire. Thus, the layer is of a simple and straightforward design, which enables a relatively cheap and easy manufacturing process of the wheel in question.
To optimize the damping, the visco-elastic layer is situated at a distance from the depth at which maximum shear occurs in the tire, said shear resulting from the contact between the tire and the railway track under rolling motion of the wheel on the track. The position to be selected depends on the load on the wheel, which defines the shear stress at each depth, and the fatigue strength of the visco-elastic material.
Said depth is selected as a compromise between the useful life of the layer, and the amount of energy dissipation required. Said dissipation and fatigue are governed by the shear stresses experienced by the visco-elastic layer. Thus, the damping can be adjusted in dependence of the field of application, as a compromise between life and vibration reduction.
In particular, the distance of the visco-elastic layer to the rolling surface of the tire may be smaller than the depth at which maximum shear occurs in the tire.
A reliable construction is obtained in case the tire comprises a main ring body carrying the flange, as well as a concentric ring body, the visco-elastic layer being interposed between the main ring body and the concentric ring body.
Said concentric ring body at the side facing away from the flange is held against coming off from the main ring body by a fixing means. In case the visco-elastic layer would be damaged, the integrity of the railway vehicle wheel in question is still guaranteed so as to provide the required safety in service.
The fixing means may be a fixing ring mounted on the main ring body. Said fixing ring may be mounted onto the main ring body by means of an interference fit.
Other mounting means could be applied as well, such as bolts or adhesives.
Moreover, at least two layers of visco-elastic material are applied, said layers being each surrounded by a concentric ring body.
The thickness of the visco-elastic layer is of a smaller order of magnitude than the thickness of the tire.
Moreover, at least two layers of visco-elastic material can be applied.